Doubt in mock exam Qs from HFEJB

[Mini Sarin]

Q-9 in HFEJB final mock exam:

Which statements concerning stateless session beans are true?
Option c) A single instance can support concurrent calls.

is not marked correct, although the spec says that a single stateless bean instance can handle concurrent calls. Is it not supposed to be this way?

Please clarify.

Thanks
Mini

[Rajan Murugan]

concurrent calls are not allowed.kindly mention the page number you are mentioning of spec.

[Mini Sarin]

Section 7.5.8 on Page 83 of the spec :-

Clients are not allowed to make concurrent calls to a stateful session object. If a client-invoked business method is in progress on an instance when another client-invoked call, from the same or different client,
arrives at the same instance of a stateful session bean class, the container may throw the java.rmi.RemoteException to the second client[7] if the client is a remote client, or the javax.ejb.EJBException if the client is a local client.
This restriction does not apply to a stateless session bean because the container routes each request to a different instance of the session bean
class.

What does the last line mean? Is concurrent access allowed or not?

Thanks
Mini

[Rajan Murugan]

Hi Mini,
you seem to be using the ejb 2.1 spec.In case you are preparing for SCBCD 1.3 then the spec is ejb 2.0.

Any stateless bean serves only one client at a time.
Refer to 103 of hfejb in case you have a copy.

" a single bean can handle multiple clients,as long as only one client at a time is in the middle of a business method invocation."

[Mini Sarin]

Hey Rajan,

Thanks for correcting. Yes I was using spec2.1

Now I am referring to the correct spec but I can see the same stmt there on Page 76 sec 7.5.6.

" a single bean can handle multiple clients,as long as only one client at a time is in the middle of a business method invocation."

What HFEJB mentions is correct, but this is what the conatiner takes care of, giving each request to a new instance. But does that mean if client tries to make concurrent calls on the stateless bean, it will get exception as it does in the case of a stateful session bean.

[Rajan Murugan]

Originally posted by Mini Sarin:
Hey Rajan,

Thanks for correcting. Yes I was using spec2.1

Now I am referring to the correct spec but I can see the same stmt there on Page 76 sec 7.5.6.



What HFEJB mentions is correct, but this is what the conatiner takes care of, giving each request to a new instance. But does that mean if client tries to make concurrent calls on the stateless bean, it will get exception as it does in the case of a stateful session bean.

How can a client call on a particular bean? When each bean is same and do not have unique identity as in stateful.Everytime you make a call a freely available bean will be picked up,if not available one is created.

[Mini Sarin]

Yes you are right. Got it, thanks.